The objectives of the proposed research are to investigate the factors involved in the packing and regulation of cell nuclei during mammalian spermatogenesis and in the formation and functioning of the male pronucleus during fertilization. Proposed experiments are designed: (1) to determine the factors involved in condensing sperm chromatin during spermiogenesis; (2) to determine the effect on spermatid template activity of changes in the protein content of spermatid nuclei; and (3) to determine the factors involved in sperm chromatin decondensation and male pronuclear formation during fertilization. The results of the proposed autoradiographic, ultrastructural and electrophoretic studies of spermatogenesis are expected to provide information on the functions of one or more of the several testis-specific proteins known to replace the histones during mammalian spermiogenesis. By employing newly developed egg microinjection methods for studies of early events of fertilization, the roles of disulfide bond reduction and proteolysis in the decondensation of the fertilization, the roles of disulfide bond reduction and proteolysis in the decondensation of the fertilizing sperm nucleus and the formation of the male pronucleus will be investigated. The results obtained from these latter studies should contribute to an understanding of critical events of early fertilization.